'Jersey Shore' Fight -- Alleged Victim Files Criminal Complaint

One of the guys who allegedly got his face bashed in by Ronnie from "Jersey Shore" last week has filed a criminal complaint with police -- and TMZ has learned, it spells big trouble for the reality star.

As we previously reported, a guy named Justin Vigerito (above) was drinking with Ronnie and Jwoww's BF last Friday at a place called Bamboo Bar in Seaside Heights, NJ. According to Justin, his friend Devon tried to join the party ... but someone from the "Shore" crew shoved him in the back, starting a huge brawl.

Justin said he went to help his friend -- and Ronnie clocked him in the face ... before punching him several more times. (Ronnie's been telling friends any punches he threw were in self-defense.)

Now, Justin has gone to cops -- filing a criminal complaint against Ronnie for assault. Seaside Heights police are investigating the incident.

But it's all bad news for Ronnie -- who enrolled in an 18-month pretrial intervention program last year, stemming from his last violent Shore encounter in 2009, when Ronnie allegedly punched another guy in the face.

The program will allow Ronnie to avoid assault charges from the 2009 incident -- but only if he completes his required community service ... and keeps his nose clean.